Method and apparatus for mitigating downlink control channel interference

ABSTRACT

A method ( 300 ) and apparatus ( 200 ) that mitigates downlink control channel interference is disclosed. The method can include receiving ( 320 ) a transmission from a network entity and determining ( 330 ) a first timing offset to transmit a downlink subframe based on the transmission received from the network entity. The method can include receiving ( 340 ) an uplink transmission from a mobile terminal and determining ( 350 ) a second timing offset based on the first timing offset and based on the received uplink transmission. The method can include transmitting ( 360 ) a timing advance command to the mobile terminal, the timing advance command including the second timing offset.

BACKGROUND

1. Field

The present disclosure is directed to a method and apparatus formitigating downlink control channel interference. More particularly, thepresent disclosure is directed to mitigating the problem of downlinkinterference from a high power base station when a lower power basestation is deployed within the coverage area of the high power basestation.

2. Introduction

Presently, in telecommunications, a heterogeneous cell, such as a ClosedSubscriber Group (CSG) cell, a hybrid cell, a femtocell, a picocell, arelay node, or other heterogeneous cell can use a small coveragecellular base station that can, for example, be used in residential orsmall business environments. It connects to a service provider networkvia a wired or wireless backhaul connection. Some heterogeneous cellsallow service providers to extend service coverage indoors, especiallywhere access would otherwise be limited or unavailable. A heterogeneouscell can also provide services to the user that may not be available ona conventional macro cell, such as, for example, mobile televisionservices or less expensive calling plan services. The heterogeneous cellincorporates the functionality of a typical base station but extends itto allow a simpler, self-contained deployment.

For example, heterogeneous cells, such as CSG cells or hybrid cells, arecells used for deployment in a campus or are individual cells used fordeployment in users' homes. The heterogeneous cells co-exist with macrocells and have a smaller coverage area than macro cells. Unlike macrocells, the heterogeneous cells are unplanned, in that the operator hasmuch less control over their placement and configuration than with macrocells.

Unfortunately, a heterogeneous cell can experience downlink interferencefrom a high power base station (eNB) for a macro-cell when a lower powerhome cell base station is deployed within the coverage area of the highpower eNB.

For example, co-channel and shared channel home-eNB (HeNB) deployments,where at least a part of the deployed bandwidth, is shared withmacro-cells are considered to be high-risk scenarios from interferencepoint-of-view. When a terminal, such as wireless user equipment,associated with, such as, connected to or camped on, a HeNB and the HeNBis deployed close to a macro-eNB (MeNB), the MeNB transmissions canseverely interfere with the terminal transmissions to the HeNB. Also,in-band decode and forward relaying involves relay nodes (RN) deployedon the same carrier as the overlay macro-cell. In order to enablebackwards compatibility, all the common control channels need to betransmitted on RN downlink.

Typically, a MeNB transmits at much higher power, such as 46 dBm for 10MHz, relative to a heterogeneous-eNB (Het-eNB or HeNB), such as 30 dBmfor RN and 20 dBm for a HeNB for 10 MHz. Therefore, the coverage of MeNBis typically larger and there exists a region, the so called exclusionzone, around the MeNB within which the transmissions from the HeNB areinterfered if a terminal happens to be connected to/camped on the HeNB.This can lead to problems both in connected mode and in idle mode suchas 1) the terminal being unable to reliably decode paging channelresulting in missed pages and therefore the inability to receiveterminal-terminated calls; 2) the terminal being unable to read commoncontrol channels; and 3) throughput degradation or degraded physicaldownlink shared channel (PDSCH) performance.

Thus, there is a need for method and apparatus that mitigates downlinkcontrol channel interference.

SUMMARY

A method and apparatus that mitigates downlink control channelinterference is disclosed. The method can include receiving atransmission from a network entity and determining a first timing offsetto transmit a downlink subframe based on the transmission received fromthe network entity. The method can include receiving an uplinktransmission from a mobile terminal and determining a second timingoffset based on the first timing offset and based on the received uplinktransmission. The method can include transmitting a timing advancecommand to the mobile terminal, the timing advance command including thesecond timing offset.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to describe the manner in which advantages and features of thedisclosure can be obtained, a more particular description of thedisclosure briefly described above will be rendered by reference tospecific embodiments thereof, which are illustrated in the appendeddrawings. Understanding that these drawings depict only typicalembodiments of the disclosure and are not therefore to be considered tobe limiting of its scope, the disclosure will be described and explainedwith additional specificity and detail through the use of theaccompanying drawings in which:

FIG. 1 illustrates an exemplary block diagram of a system in accordancewith a possible embodiment;

FIG. 2 is an exemplary block diagram of a wireless base stationaccording to a possible embodiment;

FIG. 3 is an exemplary flowchart illustrating the operation of awireless base station according to a possible embodiment;

FIG. 4 is an exemplary flowchart illustrating the operation of awireless communication device according to a possible embodiment;

FIG. 5 is an exemplary illustration of shifting a heterogeneous basestation subframe;

FIG. 6 is an exemplary illustration of offsetting a heterogeneous basestation's frame timing relative to a macro base station;

FIG. 7 is an exemplary illustration of frame timing of a heterogeneousbase station offset relative to a macro base station; and

FIG. 8 is an exemplary illustration of frame timing of a heterogeneousbase station offset relative to a macro base station.

DETAILED DESCRIPTION

FIG. 1 is an exemplary block diagram of a system 100 according to apossible embodiment. The system 100 can include a terminal 110, a firstcell 140, a first cell base station 145, a second cell 130, a secondcell base station 135, and a network controller 120. The terminal 110may be a wireless communication device, such as a wireless telephone, acellular telephone, a personal digital assistant, a pager, a personalcomputer, a selective call receiver, or any other device that is capableof sending and receiving communication signals on a network includingwireless network. The first base station 145 can be a heterogeneous cellbase station, such as a home base station or a relay node, and thesecond base station 135 can be a macro cell base station. For example, aheterogeneous cell base station can be a closed subscriber group basestation, a relay node, a femtocell base station, a picocell basestation, or any other base station that can be within a coverage area ofa macro cell base station. As a further example, the first base station145 can be a heterogeneous cell base station configured to operate atlower power than a macro cell base station 135 within a coverage area ofthe macro cell base station 135.

In an exemplary embodiment, the network controller 140 is connected tosystem 100. The controller 140 may be located at a base station, at aradio network controller, or anywhere else on the system 100. The system100 may include any type of network that is capable of sending andreceiving signals, such as wireless signals. For example, the system 100may include a wireless telecommunications network, a cellular telephonenetwork, a Time Division Multiple Access (TDMA) network, a Code DivisionMultiple Access (CDMA) network, a satellite communications network, andother like communications systems. Furthermore, the system 100 mayinclude more than one network and may include a plurality of differenttypes of networks. Thus, the system 100 may include a plurality of datanetworks, a plurality of telecommunications networks, a combination ofdata and telecommunications networks and other like communicationsystems capable of sending and receiving communication signals.

In operation, the heterogeneous cell base station 145 can receive atransmission from a network entity, such as the second cell base station135 or the network controller 120. The heterogeneous cell base station145 can determine a first timing offset to transmit a downlink subframebased on the transmission received from the network entity. Theheterogeneous cell base station 145 can receive an uplink transmissionfrom a mobile terminal 110. The heterogeneous cell base station 145 candetermine a second timing offset based on the first timing offset andbased on the received uplink transmission. The heterogeneous cell basestation 145 can transmit a timing advance command to the mobile terminal110, where the timing advance command can include the second timingoffset.

According to a related embodiment, the heterogeneous cell base station145 can receive a timing offset value from a network entity over a relaybackhaul, such as an X2 connection. The heterogeneous cell base station145 can offset frame timing of a downlink transmission relative to areference timing by an amount determined from the received timing offsetvalue. The heterogeneous cell base station 145 can transmit the downlinktransmission based on the offset frame timing.

In another embodiment, the heterogeneous cell base station 145 canreceive a timing offset value from a first wireless terminal operatingin the same network. The wireless terminal can receive a timing offsetvalue from a network entity such as a macro base station 135 and send asignal to the heterogeneous base station 145 indicating the receivedtiming offset value. The heterogeneous base station 145 can use thetiming offset signaled by the first wireless terminal for determiningthe first timing offset value. The heterogeneous base station 145 canthen receive an uplink transmission from a second wireless terminal 110and compute a second timing offset value based on the received uplinktransmission and the first timing offset value. The heterogeneous basestation 145 can signal a timing advance command to the second wireless110 terminal including the second timing offset value. As anotherexample, the wireless terminal can compute a timing offset based on atransmission from a base station and transmit information related to thetiming offset to the wireless base station. As a further example, theinformation can be relayed information received by the wireless terminalfrom the network entity and relayed via an uplink to the first wirelessbase station.

According to another related embodiment, the second base station 135 canoffset, by the second base station, downlink frame timing relative todownlink frame timing of the first base station 145. The second basestation 135 can transmit information based on the offset downlink frametiming. The first base station 145 can reduce power on a set of resourceelements in its downlink transmission that overlap in time and frequencywith a control channel transmission. The first base station 145 cantransmit information based on the reduced power.

The transmission from a second base station can be a control channeltransmission, such as a physical broadcast channel (PBCH) transmission,a synchronization channel (SCH) transmission comprising one or both of aprimary synchronization channel (P-SCH) and a secondary synchronizationchannel (S-SCH), a physical downlink control channel (PDCCH)transmission, a physical control format indicator channel (PCFICH)transmission, a physical hybrid automatic repeat request indicatorchannel (PHICH) transmission, a cell-specific reference signaltransmission, a dedicated reference signal (DRS) transmission or anothercontrol channel transmission. In one embodiment, the second base station135 can signal a timing advance value to a terminal 110 connected to thesecond base station 135 that is not less than a downlink frame timingoffset between the first base station 145 and the second base station135. In an alternate embodiment, the second base station 135 can signala timing advance value to a terminal 110 connected to the second basestation 135 that is not less than a downlink frame timing offset betweenthe first base station 145 and the second base station 135 modulo theduration of one subframe (eg. 1 ms).

FIG. 2 is an exemplary block diagram of a wireless base station 200,such as the heterogeneous base station 145, according to a possibleembodiment. The wireless base station 200 can include a base stationhousing 210, a base station controller 220 coupled to the base stationhousing 210, a transceiver 250 coupled to the housing 210, an antenna255 coupled to the transceiver 250, and a memory 270 coupled to thehousing 210. The wireless communication device 200 can also include afirst timing offset determination module 290 and a second timing offsetdetermination module 292. The first timing offset determination module290 and the second timing offset determination module 292 can be coupledto the base station controller 220, can reside within the base stationcontroller 220, can reside within the memory 270, can be autonomousmodules, can be software, can be hardware, or can be in any other formatuseful for a module on a wireless communication device 200. Thetransceiver 250 may include a transmitter and/or a receiver. The memory270 may include a random access memory, a read only memory, an opticalmemory, or any other memory that can be coupled to a wireless basestation.

In operation, the base station controller 220 can control operations ofthe wireless base station 200. The transceiver 250 can receive atransmission from a network entity, such as the network controller 120or a second base station, like the macro base station 135. For example,the second base station can be a macro base station that indicates afirst timing offset value to home base stations in its coverage area.The transmission from the network entity can be received over abackhaul, a X2 connection, a wired connection, a wireless connection, orotherwise. The transceiver 250 can receive a transmission from thesecond base station by receiving a synchronization channel from thesecond base station. For example, the synchronization channel can be aP-SCH (Primary synchronization channel) or S-SCH (Secondarysynchronization channel). As a further example, the transceiver 250 canreceive a transmission from the second base station by receiving acell-specific reference signal from the second base station. As anadditional example, the transceiver 250 can receive a transmission fromthe second base station by receiving a message over an X2 interface, themessage indicating the first timing offset value from the second basestation.

The first timing offset determination module 290 can determine a firsttiming offset to transmit a downlink subframe based on the receivedtransmission. The first timing offset determination module 290 candetermine a first timing offset by determining a first timing offset totransmit a downlink subframe based on the received transmission andbased on a reference timing of the second base station. Also, the basestation controller 220 can determine a special subframe configurationbased on the first timing offset value.

The transceiver 250 can receive an uplink transmission from a mobileterminal, such as the terminal 110. For example, the transceiver 250 canreceive an uplink transmission from the mobile terminal by receiving anuplink transmission selected from a random access channel transmissionand a sounding reference signal transmission from the mobile terminal.The second timing offset determination module 292 can determine a secondtiming offset based on the first timing offset and the received uplinktransmission. For example, the second timing offset can be a timingadvance that can be a function of the distance of the terminal from thefirst wireless base station and can be a function of the timing offset.The transceiver 250 can transmit a timing advance command to the mobileterminal, where the timing advance command can include the second timingoffset. For example, the transceiver 250 can transmit the determinedspecial subframe configuration in a System Information Broadcastmessage. The determined special subframe configuration can betransmitted in a System Information Broadcast message to multipleterminals.

FIG. 3 is an exemplary flowchart 300 illustrating the operation of awireless base station, such as the heterogeneous base station 145,according to a possible embodiment. At 310, the flowchart begins. At320, a transmission can be received from a network entity, such as thenetwork controller 120 or a second base station, like the macro basestation 135. For example, the second base station can be a macro basestation that indicates a first timing offset value to heterogeneous basestations in its coverage area. The transmission from the network entitycan be received over a backhaul, a wired connection, an X2 connection, awireless connection, or otherwise. As a further example, thetransmission can be received from the second base station by receiving asynchronization channel from the second base station. Thesynchronization channel can be a P-SCH (Primary synchronization channel)or S-SCH (Secondary synchronization channel). As another example, thetransmission can be received from the second base station by receiving acell-specific reference signal from the second base station. As anadditional example, the transmission can be received from the secondbase station by receiving a message over an X2 interface, where themessage can indicate the first timing offset value from the second basestation. Also, the transmission received from a network entity caninclude a timing offset value corresponding to a number of subframes tooffset downlink control signal transmissions to the mobile terminal. Thelast example can be useful because it can enable a macro base station ora network controller to apply a common timing offset value to all theheterogeneous base stations within a certain coverage area that allowsfor interference reduction to control channels transmission fromheterogeneous base stations. In this scenario, the macro base stationscan know which set of time-frequency resources to attenuate or mute inorder that the interference to control channel transmission fromheterogeneous base stations can be reduced.

At 330, a first timing offset can be determined to transmit a downlinksubframe based on the transmission received from the network entity. Thefirst timing offset can be determined by determining a first timingoffset to transmit a downlink subframe based on the transmissionreceived from a network entity and based on a reference timing of thesecond base station. At 340, an uplink transmission can be received froma mobile terminal For example, the uplink transmission can be receivedfrom the mobile terminal by receiving a Random Access Channel (RACH)transmission or a Sounding Reference Signal (SRS) transmission from themobile terminal.

At 350, a second timing offset can be determined based on the firsttiming offset and based on the received uplink transmission. Forexample, the second timing offset can be based on a timing advance thatis a function of the distance of the terminal 110 from the heterogeneousbase station 145 and a function of the timing offset. For example, aspecial subframe configuration can be determined based on the firsttiming offset value. At 360, a timing advance command can be transmittedto the mobile terminal. The timing advance command can include thesecond timing offset. For example, the determined special subframeconfiguration can be transmitted in a System Information Broadcastmessage. The determined special subframe configuration can betransmitted in a System Information Broadcast message to multipleterminals. Table 1 shows different possible special subframeconfigurations where DwPTS is the downlink pilot timeslot and UpPTS isthe uplink pilot timeslot.

TABLE 1 Normal cyclic prefix in Extended cyclic prefix in Spe- downlinkdownlink cial UpPTS UpPTS sub- Nor- Ex- Nor- Ex- frame mal tended maltended con- cyclic cyclic cyclic cyclic fig- prefix prefix prefix prefixura- in in in in tion DwPTS uplink uplink DwPTS uplink uplink 0  6592 ·T_(s) 2192 · 2560 ·  7680 · T_(s) 2192 · 2560 · 1 19760 · T_(s) T_(s)T_(s) 20480 · T_(s) T_(s) T_(s) 2 21952 · T_(s) 23040 · T_(s) 3 24144 ·T_(s) 25600 · T_(s) 4 26336 · T_(s)  7680 · T_(s) 4384 · 5120 · 5  6592· T_(s) 4384 · 5120 · 20480 · T_(s) T_(s) T_(s) 6 19760 · T_(s) T_(s)T_(s) 23040 · T_(s) 7 21952 · T_(s) — — — 8 24144 · T_(s) — — —

For example, there are 9 configurations which can define differentsplits for DwPTS/guard/UpPTS. The reduced guard period (GP) can bedetermined according to:

GP′=GP−k*ofdm_symbol_duration, where k is the first timing offset inOFDM symbols.

The guard period should be large enough to accommodate the heterogeneousbase station cell radius and the transmit-receive switching timerequired for terminals. For the above example, that T_(s)=(1/30720000)s.

Table 2 shows different possible uplink-downlink configurations where Dis downlink, S is special, and U is uplink.

TABLE 2 Uplink- Downlink- downlink to-Uplink config- Switch-pointSubframe number uration periodicity 0 1 2 3 4 5 6 7 8 9 0  5 ms D S U UU D S U U U 1  5 ms D S U U D D S U U D 2  5 ms D S U D D D S U D D 3 10ms D S U U U D D D D D 4 10 ms D S U U D D D D D D 5 10 ms D S U D D D DD D D 6  5 ms D S U U U D S U U D

The ratio of PDSCH energy per resource element (EPRE) to cell-specificreference signal (CRS) EPRE among PDSCH REs (not applicable to PDSCH REswith zero EPRE) for each OFDM symbol is denoted by either rho_A or rho_Baccording to the OFDM symbol index in LTE Release 8 specification. Thepower ratio rho_B can be applicable to OFDM symbols bearingcell-specific reference signal and rho_A can be applicable to OFDMsymbols without and can account for the power boosting/de-boosting inreference signal and data resource elements. A third ratio, rho_C, canaccommodate power reduction/muting on selected resource blocks on asymbol-by-symbol basis that is used by a base station (for example,macro base station) to reduce interference to the control transmissionof a heterogeneous base station. At 370, the flowchart 300 can end.

FIG. 4 is an exemplary flowchart 400 illustrating the operation of awireless communication device, such as the terminal 110, according to apossible embodiment. At 410, the flowchart begins. At 420, an indicationcan be received from a serving base station, such as the heterogeneousbase station 145. The indication can include information thattransmission power on resource elements on a set of orthogonal frequencydivision multiplexed (OFDM) symbols corresponding to a certain set ofresource blocks is different from the transmission power outside thisset. For example, the indication can be a rho_C value. As a furtherexample, a first indication can be received from a serving base station,where the first indication can include information relating totransmission power on resource elements transmitted on orthogonalfrequency division multiplexed symbols bearing cell-specific referencesignal. A second indication can be received from the serving basestation, where the second indication can include information relating tothe transmission power on resource elements transmitted on orthogonalfrequency division multiplexed symbols not bearing cell-specificreference signal. A third indication can be received from the servingbase station, where the third indication can include informationrelating to transmission power on resources on orthogonal frequencydivision multiplexed symbols corresponding to a certain set of resourceblocks. At 430, coded data transmissions can be received from theserving base station. At 440, the coded data transmissions can bedecoded based on the indication. At 450, the flowchart 400 can end.

Embodiments can provide for time-shifting heterogeneous base stationcontrol regions relative to a macro cell's control regions and havingthe macro cell attenuate or mute symbol portions that overlap theheterogeneous base station control regions.

FIG. 5 is an exemplary illustration 500 of shifting a heterogeneous basestation subframe. Frequency is based on the y-axis and time is based onthe x-axis split into resource blocks. The first two symbols canrepresent a control region, the next 12 symbols can represent availabledownlink resources, the next three symbols can represent DwPTS withcontrol region, the next ten symbols can represent a guard period (GP),the next symbols can represent UpPTS. Heterogeneous base stationsubframes can be shifted by k=2 symbols relative to macro base stationsubframes. In a related embodiment, heterogeneous base station subframescan be shifted by k=16 symbols relative to a macro base stationsubframe. When shifting by k=16 symbols, the heterogeneous base stationsynchronization channel (SCH) and physical broadcast channel (PBCH) canoccur in the next subframe.

For example, carriers can be overlapped with time shifting at a symbollevel for non-overlapped control. Heterogeneous base stationtransmissions can be time shifted by k symbols, such as to avoid overlapwith macro cell base station control regions of size k, and the macrobase station can perform power reduction or muting on the portion of asymbol (or symbols) that overlap the control region of the heterogeneousbase station.

The macro base station can also use power reduction on all the resourceblocks, such as the 25 resource blocks, overlapping the heterogeneousbase station control region to improve physical downlink shared channel(PDSCH) performance for the heterogeneous base station if theheterogeneous base station is very close to the macro base station. Forexample, if the first base station is a home base station, a singleorthogonal frequency division multiplexed (OFDM) symbol macro basestation control region with n=1 can be used for PDSCH efficiency whichcan leave 5 control channel elements for home base station controlchannels, which should be sufficient for home base station controlsignaling.

Due to the time shift of macro base station transmissions, the last ksymbols of the macro base station PDSCH region can see interference fromthe heterogeneous base station control region. The macro base stationPDSCH overlap with the heterogeneous base station control region can befurther mitigated by either (a) using truncation so that only 14-n-ksymbols can be used for the macro base station PDSCH or (b) not usingtruncation, such as using 14-n symbols, but accounting for the overlapvia modulation and coding scheme (MCS) selection.

For certain time shifts (for example, k=3 or 4), the SCH transmissionfrom the macro base station can overlap with the PBCH transmission fromthe heterogeneous base station. In one embodiment, a wireless terminalcan estimate the received signal corresponding to the SCH transmissionfrom the macro base station and cancel it from the received signal sothat interference to the PBCH transmission from the heterogeneous basestation can be reduced.

For one embodiment, since the interference to the heterogeneous basestation carrier on the macro base station packet data control channel(PDCCH) signals in the control region is being avoided by time shifting,the macro base station carrier need not be segmented. In other words,the heterogeneous base station and the macro base station can useoverlapping frequency resources or even the same carrier frequency. Themacro base station carrier can still be segmented. Carrier segmentationfor macro base station can be also avoided in another embodiment, asshown in the illustration 500, by allocating the macro base station thefull band as well, but then an additional one subframe shift with k=16total symbols can be used so that the macro base station's sharedchannel and physical broadcast channel (SCH/PBCH) do not overlap withthe heterogeneous base station's SCH/PBCH. Then macro base station canthen mute or attenuate its PDSCH symbol(s) overlapping the heterogeneousbase station control region and can also attenuate or mute the resourceblocks that overlap the heterogeneous base station's PBCH/SCH.

Radio resource management (RRM) measurements of heterogeneous basestation can be conducted as normal.

For example, the macro base station can be assumed to be time alignedwith the macro cell. The heterogeneous base station downlink subframecan be shifted by k symbols relative to macro cell downlink subframe toavoid overlap in their control regions. The macro cell can attenuate ormute symbol(s) in its PDSCH region that overlap the heterogeneous basestation control region. The macro cell can attenuate or mute physicalresource blocks (PRBs) in PDSCH region that overlap the SCH or PBCH.

FIG. 6 is an exemplary illustration 600 of offsetting a heterogeneousbase station's frame timing relative to a macro base station by k OFDMsymbols. Timing offset can be used together with uplink timing advancecontrol. This can address the control channel interference problem intime division duplex (TDD) deployments. The illustration 600 shows a TDDconfiguration of downlink, special, uplink, uplink, downlink (DSUUD)with a 5 ms downlink to uplink switch point periodicity, where DwPTSrepresents a downlink pilot timeslot, UpPTS represents an uplink pilottimeslot, and GP represents a guard period for a macro base station(eNB1) and a heterogeneous base station (eNB2). The downlink subframesfrom the heterogeneous base station are offset by k OFDM symbolsrelative to the macro base station downlink frame timing. As in aprevious example, the macro base station can perform power reduction ormuting on resource elements during which the heterogeneous base stationis transmitting its control signals.

A serving base station can apply an uplink timing advance to a terminalthat takes into the account the propagation delay between the basestation and the terminal to ensure that downlink and uplink frametiming, from the perspective of the base station antennas, are aligned.To a first order approximation, the value of the timing advance is equalto the base station-terminal propagation delay. However, the uplinktransmission from a terminal attached to heterogeneous base station canpotentially interfere on the macro base station downlink if a timingadvance is equal to the base station-terminal propagation delay, as themacro base station downlink transmission starts k symbols earlier thanthe heterogeneous base station downlink transmission. To a first orderapproximation, if the uplink timing advance of a terminal attached to aheterogeneous base station is set to base station-terminal propagationdelay+k*ofdm_symbol_duration, the terminal may not interfere with macrobase station downlink transmission. This can reduces the effective guardperiod to

GP′=GP−k*ofdm_symbol_duration

The complete avoidance of terminal uplink transmission interference withthe macro base station downlink may or may not possible depending on thespecial subframe configuration being used, such as based on the lengthsof the DwPTS and the UpPTS, as it may not always be possible to satisfythe requirement that

GP′>2*T_prop_max+rx−tx switch delay+k*ofdm_symbol_duration

Where T_prop_max=maximum MeNB UE propagation delay, a quantity that candepend on the macro cell size.

FIG. 7 is an exemplary illustration 700 of frame timing of aheterogeneous base station (eNB2) offset relative to a macro basestation (eNB1) by k=10 OFDM symbols. The eNB1 PBCH and P/S-SCHtransmission interfering with the eNB2 PBCH and P/S-SCH can becompletely avoided. However, the resulting effective guard period of oneOFDM symbol period may not be sufficient for some deployments. Theinterference from the macro base station transmission to the PDCCHtransmission from heterogeneous base station can be potentially avoidedcompletely if k>=NCtrl2, where NCtrl2 is the number of control symbolsused by the heterogeneous base station (eNB2). If k=4, the inference onP/S-SCH transmissions from eNB1 to P/S-SCH from eNB2 can be completelyavoided. Also, eNB1 PBCH to eNB2 PBCH interference can be avoided.However, eNB1 S-SCH transmission with one OFDM symbol/6 PRBs caninterfere with the eNB2 PBCH. The resulting effective guard period (GP′)might be sufficient for most cellular deployments, such as micro-urban,small cell suburban, and other cellular deployments.

FIG. 8 is an exemplary illustration 800 of frame timing of aheterogeneous base station (eNB2) offset relative to a macro basestation (eNB1) by k=71 OFDM symbols. For TDD configurations with 5 msdownlink-uplink (DL-UL) switch periodicity and that have the sameDL/special/UL subframe pattern in both the first and the second half ofthe radio frame (for example, TDD configurations 0, 1 and 2 as per Table2), an offset equal to k=71 can be applied to eNB2 together with eNB1muting or reduced power transmission on overlapping resources tocompletely avoid interference from eNB1 on PDCCH/PCFICH/PHICH/PBCH/SCHof eNB2 for the case of normal cyclic prefix subframes. For the case ofextended cyclic subframes, k=61 can be applied towards the same end.This concept of a half-subframe of 5 ms plus a fractional subframe shiftcan be applied to TDD configuration 6 with some scheduling DL/ULrestrictions on subframes 4 and 9 for either eNB1 or eNB2 or both. TheeNB1 PBCH and P/S-SCH transmission interfering with eNB2 PBCH andP/S-SCH can be completely avoided. The resulting effective guard periodis likely to be sufficient in most deployments. In an analogous fashion,other values of k with different levels of interference from eNB1 toeNB2 can be envisaged.

Different UL timing advance (TA) values can be needed for differenteNB2s depending on the physical separation between the eNB1 and eNB2.Because the principle can be to avoid interference from a terminalattached to eNB2 transmitting on its UL on to the DL of eNB1, an eNB2that is located far away from an eNB1, such as a heterogeneous basestation at a macro cell's cell edge, may need to apply larger TA valuesto its terminals as compared to the TA value required for terminalsconnected to an eNB2 that is close to eNB1. Thus, eNB1 or the networkcould signal a minimum value of TA that each eNB2 needs to apply toterminals served by it. In one example, a value TA_offset can besignaled to an eNB2, and if TA_(—)0 were the timing advance value eNB2would have applied to a UE served by it originally, as a function ofeNB2-terminal propagation delay, in order to enable the DL interferencemitigation technique presented in the above embodiments, eNB2 can nowapply a timing advance with a value equal to:

TA=TA_offset+TA_(—)0

The TA_offset indicated to different eNB2s may be different as functionof eNB1−eNB2 propagation delay.

For the case of in-band relay nodes, a control channel and higher layersignaling can exist between eNB1 and eNB2 over the base station-radionetwork (eNB-RN) backhaul. The eNB can indicate to the RN, the parameterk or alternately the amount of frame timing offset the RN should apply,such as relative to the timing of the first arriving signal path on theeNB-RN link. For the case of femto-cells and home base stations (HeNBs),an X2 link between a HeNB and a macro-eNB may not exist. However,E-UTRAN architectures where an X2 or a similar link between every HeNBand either a HeNB gateway (GW) or a eNB may be used. The network cansignal the timing offset parameter that a HeNB should apply to its DLtransmissions, such as relative to the timing of the first arrivingsignal path on the eNB-RN link. For both HeNB and relay nodes (RN), thenetwork can signal the offset that eNB2 should apply to the timingadvance for its terminals. This signaling can be transported over theeNB-RN backhaul for in-band relays and over X2 or a similar interfacefor femto-cells/HeNBs.

In the above embodiments, a macro cell eNB1 can power down or mutetransmissions corresponding to PDSCH resource elements that interferewith P/S-SCH, PBCH, and/or PDSCH transmissions from a heterogeneous celleNB2 (RN/HeNB). The interfering eNB1 can reduce power down or mute, suchas not allocate DL resources to any terminal, resource blocks (RBs) thatoverlap with P/S-SCH or PBCH of eNB2. For the case of PDSCH, eNB1 canstatically allocate certain low interference RBs where it can eitherreduce power or mute so that eNB2 can schedule its users on the DL inthat set.

Reducing power or muting at a RB level granularity can have an advantagethat it is Rel-8 compliant. However, a certain number of RBs can have amaximum power constraint or are blocked from transmission. In order tomitigate this, power reduction or muting at a symbol level granularitycan be used.

For the case of muting/down-rating power of selected resource elements(REs) when symbol level granularity is used, such as when the macro cellmutes only a few symbols over just the center 6 PRBs to avoidinterfering with HeNB SCH or PBCH, power reduction/muting can be enabledwith some simple signaling sent over the system information (SI) orradio resource control (RRC).

For example, for each symbol in a subframe, denote by rho_C the ratio ofPDSCH energy per resource element (EPRE) for certain RBs on symbols withindices in set S to cell-specific reference signal EPRE. For each entryin set S, such as the symbol index, the start RB index and the end RBindex for which rho_C is applicable can be indicated. For the remainderof the RBs, the existing Rel-8 PDSCH EPRE structure, obtained from rho_Aand rho_B can be maintained. The allowed set of values for rho_C caninclude zero to include the possibility of muting.

Since this pattern is likely periodic, one can signal; 1) one patternthat is common to all subframes; 2) one pattern for SF#0, while theremainder of the subframes use a second pattern, such as a total of twopatterns; 3) one pattern each for SF#0 or SF#5 and a third one for theremainder of the subframes for a total of three patterns; or 4) onepattern for each subframe in the radio frame. Note that the patternrepetition periodicity is 10 ms is all of the above cases. Patterns withperiodicities other than the above can be envisaged.

There is no need for defining new TBS or interleaving. Since the signalindicates which set of RBs are punctured on a per-symbol basis, a simplemodification can suffice to accommodate this change where for each ofthe antenna ports used for transmission of the physical channel, theblock of complex-valued symbols y^((p))(0), . . . , y^((p))(M^(ap)_(symb)−1) can be mapped in sequence starting with y^((p))(0) toresource elements (k, l) which meet the following criteria: 1) they arein the physical resource blocks corresponding to the virtual resourceblocks assigned for transmission; 2) they are not used for transmissionof PBCH, synchronization signals or reference signals; 3) they are notin resource elements for which rho_C=0; and 4) they are not in an OFDMsymbol used for PDCCH.

The methods of this disclosure may be implemented on a programmedprocessor. However, the operations of the embodiments may also beimplemented on a general purpose or special purpose computer, aprogrammed microprocessor or microcontroller and peripheral integratedcircuit elements, an integrated circuit, a hardware electronic or logiccircuit such as a discrete element circuit, a programmable logic device,or the like. In general, any device on which resides a finite statemachine capable of implementing the operations of the embodiments may beused to implement the processor functions of this disclosure.

While this disclosure has been described with specific embodimentsthereof, it is evident that many alternatives, modifications, andvariations will be apparent to those skilled in the art. For example,various components of the embodiments may be interchanged, added, orsubstituted in the other embodiments. Also, all of the elements of eachfigure are not necessary for operation of the disclosed embodiments. Forexample, one of ordinary skill in the art of the disclosed embodimentswould be enabled to make and use the teachings of the disclosure bysimply employing the elements of the independent claims. Accordingly,the embodiments of the disclosure as set forth herein are intended to beillustrative, not limiting. Various changes may be made withoutdeparting from the spirit and scope of the disclosure.

In this document, relational terms such as “first,” “second,” and thelike may be used solely to distinguish one entity or action from anotherentity or action without necessarily requiring or implying any actualsuch relationship or order between such entities or actions. Also,relational terms, such as “top,” “bottom,” “front,” “back,”“horizontal,” “vertical,” and the like may be used solely to distinguisha spatial orientation of elements relative to each other and withoutnecessarily implying a spatial orientation relative to any otherphysical coordinate system. The terms “comprises,” “comprising,” or anyother variation thereof, are intended to cover a non-exclusiveinclusion, such that a process, method, article, or apparatus thatcomprises a list of elements does not include only those elements butmay include other elements not expressly listed or inherent to suchprocess, method, article, or apparatus. An element proceeded by “a,”“an,” or the like does not, without more constraints, preclude theexistence of additional identical elements in the process, method,article, or apparatus that comprises the element. Also, the term“another” is defined as at least a second or more. The terms“including,” “having,” and the like, as used herein, are defined as“comprising.”

We claim:
 1. A method in a wireless terminal, the method comprising:receiving an indication from a serving base station, the indicationincluding information relating to zero transmission power on a first setof resource elements within orthogonal frequency division multiplexedsymbols of a subframe; receiving a coded packet transmission wherein thecoded packet transmission is embedded in a block of complex-valuedsymbols y(p)(0),. . ., y(p)(Msymb(p)−1), wherein the block ofcomplex-valued symbols are be mapped in sequence starting with y(p)(0)to resource elements such that: the resource elements are in thephysical resource blocks corresponding to the virtual resource blocksassigned for transmission, the resource elements are not used fortransmission of a physical broadcast channel, synchronization signals,or reference signals, the resource elements do not belong to a first setof resource elements that correspond to zero transmit power as suggestedby the indication received from the serving base station, and theresource elements are not in an orthogonal frequency divisionmultiplexed symbol used for a physical downlink control channel; anddecoding the coded packet transmission based on the indication.
 2. Themethod of claim 1, wherein the indication from the serving base stationis received on one of a radio resource control message and a systeminformation broadcast message.
 3. The method of claim 1, wherein theindication from the serving base station includes information relatingto zero power resources on orthogonal frequency division multiplexedsymbols corresponding to a certain set of resource blocks.
 4. The methodof claim 1, wherein the indication from the serving base stationincludes information relating to zero power resources on a subset S oforthogonal frequency division multiplexed symbols within a subframe. 5.The method of claim 1, wherein the indication from the serving basestation includes information relating to the subset S of orthogonalfrequency division multiplexed symbols within a subframe.
 6. The methodof claim 1, wherein the indication from the serving base station isassociated with a periodic subframe pattern.